Add extra prompts, endless generation, random character default, and small fixes

- Add extra positive/negative prompt textareas to all 9 detail pages with session persistence
- Add Endless generation button to all detail pages (continuous preview generation until stopped)
- Default character selector to "Random Character" on all secondary detail pages
- Fix queue clear endpoint (remove spurious auth check)
- Refactor app.py into routes/ and services/ modules
- Update CLAUDE.md with new architecture documentation
- Various data file updates and cleanup

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

data/characters/yuffie_kisaragi.json

@@ -15,7 +15,7 @@
   },
   "defaults": {
     "expression": "cheeky smile",
-    "pose": "holding glass orb, materia",
+    "pose": "wave",
     "scene": "forest, sunlight"
   },
   "wardrobe": {
@@ -27,7 +27,7 @@
       "legwear": "single kneehigh sock",
       "footwear": "boots, ",
       "hands": "fingerless glove on one hand, large gauntlet on one arm",
-      "accessories": "shuriken"
+      "accessories": "shuriken, materia"
     }
   },
   "styles": {
@@ -46,4 +46,4 @@
   "tags": [
     "Final Fantasy VII"
   ]
-}
+}